Exemplary embodiments relate generally to an integrated circuit, and more particularly to a voltage generator and a method of generating a voltage for operating a semiconductor memory device.
A semiconductor memory devices such as a flash memory device includes a voltage generator for generating high voltage within a chip. The voltage generator is configured to output high voltage by pumping low voltage through a pumping operation.
The voltage generator includes a plurality of charge pump circuits coupled in series and generates target voltage in such a manner that voltage raised by a charge pump circuit of a previous stage is raised by a charge pump circuit of a next stage in response to an input clock.
A regulator is necessary to maintain the output voltage of the charge pump circuits at a target level. In general, the regulator compares voltage, divided from the output voltage of the charge pump circuit by a resistor, with a reference voltage. If, as a result of the comparison, the output voltage is lower than the reference voltage, the regulator drives the charge pump circuit. If, as a result of the comparison, the divided voltage becomes higher than the reference voltage, the regulator stops the pumping operation of the charge pump circuit.
A known voltage generator performs a pumping operation in response to a clock signal having a constant cycle. Therefore, pump drivability and a pumping voltage rising time may vary depending on the load.